Aliphatic acyl transferase genes

ABSTRACT

A protein which has an amino acid sequence shown by SEQ ID NO: 2, 4, 6, 23, 25, 27 or 29, or any of these amino acid sequences modified, and which has activity for transferring an aliphatic acyl group to a glycosyl group at the 5-position of flavonoids, and a gene encoding the same.

FIELD OF THE INVENTION

The present invention relates to a gene encoding a protein which has an activity to transfer an aliphatic acyl group to a glycosyl group at the 5-position of flavonoids, and to a method of using same.

RELATED ART

In the floriculture industry, it is important to develop new and different varieties of flowering plants. In particular, flower colour is one of the most important characteristics of flowering plants, and classical breeding techniques that rely on crossing have been used extensively to develop new varieties exhibiting various colours. However, since genetic resources are very limited for a particular plant species in which crossing can be carried out, it is rare for a single plant species to have a full spectrum of colour varieties.

Flower colour is predominantly due to a class of compounds, generally called anthocyanins, which belong to flavonoids. It has been known that there are various anthocyanins in plants, and the molecular structure of many of these compounds have already been determined. The colour of an anthocyanin is determined mainly by its structure (Harborne (1986) The Flavonoids, p. 565). Research has been conducted on enzymes, and genes encoding these enzymes, involved in biosynthesis of anthocyanins. There are instances, for example, in which techniques in molecular biology were applied, and genes were introduced into plants to alter flower colours (Holton et al. (1995) Plant Cell, 7, p. 1071; Tanaka et al. (1998) Plant Cell Physiol. 39. p. 1119). The biochemical pathway for biosynthesis of anthocyanins up to anthocyanidin 3-glucosides is common in most flowering plats (Holton et al. (1995) Plant Cell, 7, p. 1071). Thereafter, anthocyanidin 3-glucosides present in plants are subjected to diverse modifications specific to species or varieties. The diversity of this modification is one of the causes for the diversity of flower colours.

Although anthocyanins are unstable compounds in neutral solution, their stability is improved by modification with a glycosyl or an acyl group (Forkmann (1991) Plant Breeding, 106, p. 1). The colour of anthocynins becomes a little reddish by glycosylation, and becomes blue when an aromatic acyl group is added (Forkmann (1991) Plant Breeding, 106, p 1). The acyl groups are broadly divided into the aromatic acyl groups (for example, the caffeoyl group, the coumaroyl group, etc.) and the aliphatic acyl groups (for example, the malonyl group, the acetyl group, etc.). The physiological role of the aliphatic acyl group as concerns flower colour is not known, except that it increases the solubility of anthocyanins.

Several studies have been reported on purification and biochemical properties of enzymes having an activity to transfer an aliphatic acyl group to anthocyanins [Archives of Biochemistry and Biophysics, 1981, 208, 233–241 (Crude purification, molecular weight, and examination of substrate-specificity of Flavonol 3MaT (an enzyme catalyzing the reaction of transferring a malonyl group to a glycosyl group at the 3-position of a flavonol) and Flavone/Flavonol 7 MaT (an enzyme catalyzing the reaction of transferring a malonyl group to a glycosyl group at the 7-position of flavone and flavonol) of parsley); Archives of Biochemistry and Biophysics, 1983, 224, 261–271 (Measurement of activity of flavonol 3MaT and Flavone/Flavonol 7 MaT in various organs of parsley); Archives of Biochemistry and Biophysics, 1983, 226, 206–217 (Purification into single sample of Flavonol 3MaT and Flavone/Flavonol 7 MaT of parsley, and Preparation of 3MaT antibody); Eur. J. Biochem. 1983, 133, 439–448 (Confirmation of existence and structure of malonylated apigenin 7-0-glucoside in parsley by means of NMR etc.); Archives of Biochemistry and Biophysics, 1984, 234, 513–521 (Determination of optimum pH, molecular weight and Km of 7MaT for an isoflavone of a pea); Phytochemistry, 1993, 32, 1425–1426 (Confirmation of existence of aliphatic acyl transferase activity to cyanidin 3-glucoside in the crude extract from flower petals of Dendranthema morifolium, a plant belonging to Asteraceae); Plant Science, 1996, 118, 109–118 (Confirmation of malonyl transferase activity in crude extract from cultured cells of Ajuca reptans); Phytochemistry, 1999, 52, 15–18 (Determination of substrate specificity of malonyl transferase derived from flower petals of dahlia)]. However, the primary structures of the proteins has not been determined, nor has cloning of the gene been reported.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to determine an effect of malonylation among acylation, by an aliphatic acyl transferase for transferring an acyl groups to anthocyanins upon colour of flowers, and to provide a gene which encodes a protein having an activity to transfer an aliphatic acyl group, preferably a gene which encodes a protein having an activity to transfer an aliphatic acyl group to anthocynins. It is possible to alter the colour of flowers by introducing a gene which encodes a protein having an activity to transfer an aliphatic acyl group, in accordance with the present invention, into a plant and by expressing the same.

As described above, there have been no reports on the effect of malonylation of anthocyanins upon flower colour. In order to determine this effect, the colour of three solutions of anthocyanins, that is, delphinidin 3,5-diglucoside, awobanin(delphinidin 3-(coumaroyl) glucoside-5-glucoside), malonyl-awobanin(delphinidin 3-(coumaroyl) glucoside-5-(malonyl)glucoside), was compared, and it was found that the colour of malonyl-awobanin is the bluest, indicating that malonylation causes anthocyanins to become bluer.

Thus, purification of a malonyl transferase was attempted using flowers of salvia as the material. Then, a partial amino acid sequences of the purified protein were determined, and based on this information, a DNA fragment of the gene encoding the malonyl transferase of salvia was amplified using the PCR method. Using this DNA fragment as a probe, the cDNA library of flower of Salvia guaranitica was screened, and two genes encoding malonyl transferase were obtained. Further, using these genes as probes, homologs were obtained from Salvia splendens, perilla, and lavender.

Therefore, according to the present invention, there is provided a gene encoding a protein which has an amino acid sequence according to any one of SEQ ID NO: 2, 4, 6, 23, 25, 27 or 29, and has an activity to transfer an aliphatic acyl group to a glycosyl group at the 5-position of flavonoids, or a gene encoding a protein which has any of these sequences modified by addition or deletion of one or more amino acids and/or substitution by other amino acids, and has activity for transferring an aliphatic acyl group to a glycosyl group at 5-position of flavonoids.

According to the present invention, there is also provided a gene encoding a protein which has an amino acid sequence exhibiting homology of 50% or more with any of the sequences according to SEQ ID NO: 2, 4, 6, 23, 25, 27 or 29, and has an activity to transfer an aliphatic acyl group to a glycosyl group at the 5-position of a flavonoids.

Further, according to the present invention, there is provided a gene which hybridizes to a part or all of the nucleotide sequences encoding any of the amino acid sequences according to SEQ ID NO: 2, 4, 6, 23, 25, 27 or 29 under the condition of 5×SSC, 50° C., and which encodes a protein having an activity to transfer an aliphatic acyl group to a glycosyl group at 5-position of flavonoids.

The present invention additionally provides a vector comprising the above-described gene.

The present invention also provides a host transformed by the above-described vector.

The present invention further provides a protein encoded by any of the above-described genes.

The present invention also provides a method of making the protein, comprising the steps of: culturing, or growing, the above-described host; and collecting, from the host, the protein having an activity to transfer an aliphatic acyl group to a glycosyl group at 5-position of flavonoids.

The present invention further provides a transgenic plant having the above-described gene introduced, or offspring of the plant or tissue thereof having the same property.

The present invention further provides a cut flower of the above-described plant or offspring thereof having the same property.

The present invention further provides a method of altering flower colour using the above-described gene.

The present invention further provides a method of making a flower blue by using the above-described gene.

PREFERRED EMBODIMENTS OF THE INVENTION

Genes of the present invention include, for example, those encoding amino acid sequences according to SEQ ID NO: 2, 4, 6, 23, 25, 27 and 29. However, it is known that a protein having an amino acid sequence that is modified by addition or deletion of plural amino acids and/or by substitution of other amino acids, exhibits the same enzyme activity as the original protein. Therefore, a protein having an amino acid sequence according to any one of SEQ ID NO: 2, 4, 6, 23, 25, 27 or 29 modified by addition or deletion of one or more amino acids and/or by substitution by other amino acids, and a gene encoding the protein, is within the scope of the present invention, as long as the protein has an activity to transfer an aliphatic acyl group to a glycosyl group at the 5-position of flavonoids.

The present invention also relates to a gene which hybridizes with a nucleotide sequence encoding amino acid sequences according to any one of SEQ ID NO: 2, 4, 6, 23, 25, 27 or 29, or a part of the nucleotide sequences, preferably a nucleotide sequence encoding 6 or more amino acids, for example, 6 or more amino acids in a concensus region, under the condition of, for example, 5×SSC, at 50° C., and which encodes a protein having an activity to transfer an aliphatic acyl group to a glycosyl group at the 5-position of flavonoids. A suitable hybridization temperature varies with the nucleotide sequence or the length thereof, and a temperature of 50° C. or lower is preferred when the probe is a DNA fragment of 18 bases encoding 6 amino acids.

Genes selected by such hybridization include naturally-occurring genes, including, but not limited to, genes derived from plants such as genes derived from petunia, torenia, etc. Also, a gene selected by hybridization may be either cDNA, or genome DNA.

Further, the present invention also relates to the use for altering flower colour, of a gene encoding a protein which has an amino acid sequence having a homology of about 50% or more, preferably 60% or 70% or more, further preferably 80% or 90% or more, with the amino acid sequence according to any one of SEQ ID NO: 2, 4, 6, 23, 25, 27 or 29, and which has an activity to transfer an aliphatic acyl group to a glycosyl group at the 5-position of flavonoids.

A gene having a native nucleotide sequence can be obtained, for example, by screening of a cDNA library, as shown more specifically in Examples. A DNA encoding a protein having a modified amino acid sequence can be synthesized starting from DNA having a native nucleotide sequence by means of usual methods such as a site-specific mutagenesis or the PCR method. For example, a DNA fragment to which a desired modification is to be introduced is first obtained by treatment of a native cDNA or genome DNA with restriction enzymes. Then, using this as a template, site-specific mutagenesis or the PCR method is performed with a primer having the desired mutation introduced therein, to obtain a DNA fragment having the desired modification introduced therein. Thereafter, the DNA fragment having the desired modification introduced therein may be ligated to a DNA fragment encoding other portions of the target protein.

Alternatively, in order to obtain DNA encoding a protein which has a shortened amino acid sequence, DNA encoding an amino acid sequence longer than the target amino acid sequence, such as the DNA encoding the full-length amino acid sequence, may be cut with suitable restriction enzymes. If the resulting DNA fragment does not encode the entire target amino acid sequence, a DNA fragment consisting of the missing sequence may be synthesized and ligated.

By expressing the obtained gene using a gene expression system in Escherichia coli and yeast, and by measuring the enzyme activity, it is possible to confirm that an obtained gene encodes a protein having an activity to transfer an aliphatic acyl group. It is also possible by expressing the gene to obtain, as a gene product, a protein having an activity to transfer an aliphatic acyl group. It is also possible by using an antibody to an amino acid sequence according to SEQ ID NO: 2, 4, 6, 23, 25, 27 or 29, to obtain a protein having an activity to transfer an aliphatic acyl group. Further, it is possible to use an antibody to clone a gene encoding a protein having an activity to transfer an aliphatic acyl group derived from other living organisms.

Therefore, the present invention relates to a recombination vector, especially an expression vector, comprising above described gene, and to a host transformed by the vector. Both procaryote and eukaryote may be used as a host. In procaryote, bacteria such as Escherichia coli that belongs to the genus Escherichia, or Bacillus subtilis that belongs to the genus Bacillus may be used as a usual host. As a eukaryotic host, a lower eukaryote, for example, a eukaryotic micro-organism such as yeast and fungi which belong to the fungi may be used.

In yeast, a micro-organism belonging to the genus Saccharomyces such as Saccharomyces cerevisiae or the like may be used as a host. In mold fungi, a micro-organism belonging to the genus Aspergillus such as Aspergillus oryzae, Aspergillus niger, and a micro-organism belonging to the genus Penicillium, may be used as hosts. Animal cells and plant cells may also be used as hosts. In animal cells, cell systems derived from a mouse, hamster, monkey, a human, etc. may be used. Insect cells such as silkworm cells, or even an adult silkworm itself, may be used as a host.

The expression vector of the present invention includes expression control regions depending upon the kind of host to which it is to be introduced, such as a promotor and a terminator, replication origin, and the like. As a promotor for an expression vector in bacteria, commonly used promotors such as a trc promotor, tac promotor, lac promotor or the like may be used. As a promotor for an expression vector in yeast, glyceraldehyde-3-phosphate dehydrogenase promotor, pH 05 promoter or the like, and as a promotor for an expression vector in fungi, an amylase promotor, a trpC promotor or the like may be used. As a promotor for an expression vector in animal cell hosts, a viral promotor such as SV 40 early promotor, SV 40 late promotor, or the like may be used. Construction of the expression vector may be performed in accordance with any of the usual methods known to those skilled in the art using restriction enzymes, ligases, etc. Transformation of host cells with the expression vector may also be performed in accordance with any of the usual methods.

The target protein can be obtained by culturing, raising or growing the host transformed with the above described expression vector, and by recovering a gene product from the culture or the like, and purifying in accordance with usual methods, for example filtration, centrifuging, disruption of cells, gel filtration chromatography, ion exchange chromatography, and the like.

The present invention is not limited to a gene derived from salvia and encoding a protein which has an activity to transfer an aliphatic acyl group. The present invention relates to use of a gene encoding a protein which has activity for transferring an aliphatic acyl group. The origin of the protein having an activity to transfer an aliphatic acyl group may be plants, animals, or microorganisms. Irrespective of the origin, such a protein can be equally applied to alteration of flower colour, as long as it has activity for transferring an aliphatic acyl group. Further, the present invention relates to a transgenic plant or its offspring or tissue thereof, including cut flowers, which is obtained by introducing a gene encoding a protein having activity to transfer an aliphatic acyl group, and which has its hue thereby modified.

By using the gene obtained according to the present invention, which encodes a protein having an activity to transfer an aliphatic acyl group, anthocyanins accumulated in vacuoles can be acylated so as to become blue, and as a result, flower colour can be altered to blue. In the present state of the art, it is possible to introduce a gene into a plant and to cause the gene to be expressed in a constitutive or tissue-specific fashion. It is also possible to suppress the expression of a target gene using, for example, an anti-sense method or a co-suppression method.

Examples of plants that can be transformed in this manner include, but are not limited to, roses, chrysanthemums, carnations, snapdragons, cyclamens, orchids, lisianthus, freesias, gerberas, gladiolus, gypsophila, kalanchoes, lilies, pelargoniums, geraniums, petunias, torenias, tulips, rice, barley, wheat, rapeseed, potatos, tomatos, poplars, bananas, eucalyptuses, sweet potatos, soybeans, alfalfa, lupine, and corn.

EXAMPLES

The present invention will be described in detail below in accordance with Examples thereof. Unless otherwise specified, the molecular biological techniques employed are those set forth in Molecular Cloning (Sambrook et al., 1989).

Example 1

Change of Colour of Various Anthocyanins Depending Upon pH

Delphinidin 3,5-diglucoside, awobanin (delphinidin 3-(coumaroyl) glucoside-5-glucoside), malonyl-awobanin (delphinidin 3-(coumaroyl)glucoside-5-(malonyl) glucoside) were dissolved in McIlvaine buffer (pH 5.3, pH 5.6, pH 6.0) in concentrations of 0.1 mM, 0.3 mM, 0.5 mM, respectively, and colours of the solutions were evaluated using Colour charts (Royal Horticulture Society). Delphinidin 3,5-diglucoside can be obtained from its 3,5-diacetylglucoside form by removing the acetyl portion in alkaline hydrolysis reaction (Tetrahedron, 48, 4313–4326, 1992).

Awobanin can be obtained from malonyl-awobanin by removing its 5-malonyl portion (Tetrahedron Lett. 24, 4863–4866, 1983). Malonyl-awobanin was obtained by extraction from plants using the method as set forth in Tetrahedron Lett. 24, 4863–4866, 1983. The greater the number in the Colour chart, the bluer the colour is. When the number is the same, symbol A represents the bluest colour. The results of the test are summarized in Table 1. In all concentrations and pH, malonyl-awobanin was the bluest, indicating that the malonyl group caused anthocyanins to become blue.

TABLE 1 Number Number in Colour Number in in Colour chart Colour chart chart Anthocyanins Concentration at pH 5.3 at pH 5.6 at pH 6.0 Delphinidin 0.1 mM 84C 84C too faint to 3,5- be measured diglucoside Delphinidin 0.3 mM 85A 86D 88C 3,5- diglucoside Delphinidin 0.5 mM 86D 90B 88B/C 3,5- diglucoside Awobanin 0.1 mM 85C 85A 91B Awobanin 0.3 mM 86D not tested 91A Malonyl- 0.1 mM 85C 91B 91B awobanin Malonyl- 0.3 mM 92A 93B 96C awobanin Malonyl- 0.5 mM 93B not tested 96A awobanin

Example 2

Measurement of Activity of Malonyl Transferase of Salvia

Measurement of activity of malonyl transferase was conducted using reaction solution 100 μl (potassium phosphate of final concentration of 20 mM, pH 7.0, containing shisonin 10 μg, malonyl CoA 10 μg, and an enzyme sample to be measured, dissolved in 0.01% trifluoro acetic acid). After reaction was carried out at 30° C. for 20 minutes, the reaction was terminated by adding 200 μl of 0.05% TFA aqueous solution cooled on ice. Quantification of shisonin and malonyl-shisonin was conducted by reverse phase high performance liquid chromatography (DYNAMAX HPLC system) using a Shodex Asahipak ODP-50 4E column, and using a linear concentration gradient with 0.5% TFA solution as the solution and 0.5% TFA, 50% acetonitrile aqueous solution as the solution, such that concentration of the B solution was 45%, 45%, 55%, 100%, 100%, 45%, and 45%, at time 0, 3, 17, 18, 23, 24, and 30 minutes, respectively, after the start of separation, at a flow rate of 0.7 ml/min, using 50 μl of reaction solution, monitoring absorption at 520 nm.

Example 3

Protein Purification of Malonyl Transferase of Salvia

Purification of malonyl transferase was conducted using red flowers 2,644 g of Salvia splendens as starting material. Flowers of salvia were collected in its entirety including calyces immediately before blossom, and were stored at −80° C. until use in experiments.

To 500 g of salvia flowers, polyvinylpolypyrrolidone (PvPP) 100 g, extraction buffer (100 mM potassium phosphate (pH 7.0), 30 mM 2-mercaptoethanol, 5 mM EDTA) 3 L and phenylmethylsulfonylfluoride (PMSF) of a final concentration 0.5 mM were added, and powdered with a HEAVY DUTY BLENDER (WARING). The solution containing the powdered material was centrifuged at 7,500×G for 20 minutes. Supernatant was filtered under reduced pressure (filter paper, Whatman 114) to obtain a crude enzyme solution. A crude enzyme solution of 10.4 L was obtained from flowers of 2,664 g.

Next, ammonium sulfate fractionation was conducted, and an enzyme was recovered as precipitation in 20% to 50% saturated ammonium sulfate fraction and dissolved in buffer A (100 mM potassium phosphate (pH 7.0), 30 mM 2-mercaptoethanol, 1 mM EDTA, 0.1 mM PMSF)(2920 ml). 280 ml of Octyl Sepharose Fast Flow (Amersham Pharmacia Biotech Co.) was added to this, and ammonium sulfate was slowly added to a final concentration of 30% saturation while the solution was slowly stirred. After adequate stirring, the solution was allowed to stand still overnight. After confirming that enzyme activity of malonyl transferase was not left in the supernatant liquid, the gel in the sludge was recovered by filtration under reduced pressure (filter paper, Whatman 114). The gel was extensively washed with buffer B (20 mM potassium phosphate (pH 7.0), 30 mM 2-mercaptoethanol, 20% saturated ammonium sulfate), while being filtered under reduced pressure.

280 ml of buffer C [20 mM potassium phosphate (pH 7.0), 15 mM 2-mercaptoethanol, 50% ethylene glycol, 0.1% 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS)] was added to the gel, and after being gently stirred for 30 minutes, a malonyl transferase active fraction was recovered by filtration under reduced pressure. This elution operation with buffer C was repeated 10 times to collect an active fraction. After the active fraction was concentrated using Pellicon (Biomax 8K, MILLIPORE CORPORATION), and was desalted in buffer D (10 mM potassium phosphate (pH 7.0), 15 mM 2-mercaptoethanol, 0.03% TritonX-100), 155 ml of enzyme solution 1 was obtained.

MIMETIC Yellow 2 (Nacalai Tesque Co.) 100 ml was loaded to Econocolumn (φ1.0 cm×120 cm, Japan Bio Rad Laboratories Co.), and was equilibrated with buffer D. After the total amount of the enzyme solution 1 was applied and washed with buffer D, protein bound to the column was eluted using buffer E (20 mM potassium phosphate (pH 7.0), 30 mM 2-mercaptoethanol, 0.05% CHAPS). The active fraction was concentrated using Pellicon and ultrafiltration (YM-10, MILLIPORE CORPORATION), and 32 ml of enzyme solution 2 was obtained.

MIMETIC Red 3 (Nacalai Tesque Co.) 50 ml was loaded to Econocolumn (φ1.5 cm×30 cm, Japan Bio Rad Laboratories Co.), and was equilibrated with buffer F (5 mM potassium phosphate (pH 7.0), 15 mM 2-mercaptoethanol, 0.03% TritonX-100). After the total amount of enzyme solution 2 was applied and washed with buffer F, the proteins bound to the column were eluted using buffer G (5 mM potassium phosphate (pH 7.0), 30 mM 2-mercaptoethanol, 0.03% TritonX-100, 0.1 mM acetylCoA). After the active fraction was concentrated using Pellicon, ultrafiltration, and Centricon, it was desalted using buffer H (30 mM potassium phosphate (pH 7.0), 30 mM 2-mercaptoethanol, 0.03% TritonX-100), and 3 ml of enzyme solution 3 was obtained.

MIMETIC Red 3 (Nacalai Tesque Co.) 5 ml was loaded to Econocolumn (φ1.0 cm×10 cm, Japan Bio Rad Laboratories Co.), and was equilibrated with buffer F. After the total amount of the enzyme solution 3 was applied and washed with buffer F, the proteins bound to the column were eluted using buffer G. After the active fraction was concentrated using Centricon, 1.5 ml of enzyme solution 4 was obtained.

After a MonoQ5/5 column (Amersham Pharmacia Biotech Co.) was equilibrated with buffer G, the total amount of the enzyme solution 4 was applied at a flow rate of 0.05 ml/min and was washed with buffer F (flow rate 0.05 ml/min for 60 minutes). The proteins bound to the column were eluted using a 0 to 100% linear gradient (flow rate 0.05 ml/min, for 400 min) formed with buffer I (20 mM potassium phosphate (pH 7.0), 30 mM 2-mercaptoethanol, 0.03% TritonX-100, 1 mM NaCl), and after the active fraction was concentrated using Centricon, 0.8 ml of enzyme solution 5 was obtained.

After Phenyl Superose HR 5/5 (Amersham Pharmacia Biotech Co.) was equilibrated with buffer B, the enzyme solution 5 having ammonium sulfate added to a final concentration of 20% saturation was applied at a flow rate of 0.02 ml/min. After the column was washed with buffer B, the proteins bound to the column were eluted using a 0 to 100% linear gradient formed with buffer C (flow rate of 0.02 ml/min, for 500 minutes), and the active fraction was obtained.

Further, a preparative electrophoresis system (Bio Phoresis III, Atto Co.) was used for fractionation, and the obtained fraction of 3.2 ml of malonyl transferase was concentrated to 40 μl using ultrafiltration membrane concentration, with substituting with 0.02% SDS/75 mM Tris-HCl buffer (pH 8.8). Thereafter, final purification was performed using a reverse phase column (PorosR2H, Japan Perceptive Co.) HPLC. Separation was conducted under the condition of a linear concentration gradient in 0.1% TFA formed by an acetonitrile concentration from 8% to 80%, at a flow rate of 0.1 ml/min for 60 minutes, and monitoring absorption at 280 nm, only the peak fraction was recovered. Since the protein finally obtained turned out to be a single band of 47 kDa, it was determined that the molecular weight of the malonyl transferase was 47 kDa.

Example 4

Determination of Partial Amino Acid Sequences of the Malonyl Transferase of Salvia

2 pmol of trypsin (Promega Co.) was added to the protein that was recovered in Example 3 as a single band. The protein was digested at 37° C. for 30 hours, and determination of the structure of each peptide fragment was attempted. Solution digested by trypsin was separated using reverse phase HPLC (μRPC C2/C18, Amersham Pharmacia Biotech Co.) into each peptide fragment. Separation was conducted under 0.1% trifluoroacetic acid using a linear concentration gradient formed with acetonitrile concentration from 8% to 80% for 60 minutes at a flow rate of 0.1 ml/min, and, while monitoring absorption at 215 nm, only absorption peak fractions were collected.

Each peak fraction was concentrated and dried by speed-back, and was dissolved in 30 μl of 37% acetonitrile and subjected to analysis using an amino acid sequencer (PSQ-1, Shimadzu Corporation). As a result, amino acid sequences of 12 peptides were obtained. The amino acid sequences are shown below.

-   MTT20: Tyr-Ala-Ala-Gly-Asp-Ser-Val-Pro-Val-Thr-Ile-Ala-Ala-Ser-Asn     (SEQ ID NO: 7) -   MTT21-1: Leu-Leu-Phe-Tyr-His-His-Pro-Ser-Ser-Lys (SEQ ID NO: 8) -   MTT21-2:     Ser-Gly-Asp-Lys-Ser-Asp-Glu-Asn-Ala-Pro-Glu-Leu-Phe-Ile-Ile-Pro-Ala-Asp-Ala     (SEQ ID NO: 9) -   MTT22-1: Met-Ala-Ala-Phe-Glu-Glu-Val-Phe (SEQ ID NO: 10) -   MTT23: Trp-Leu-His-Tyr-His-Pro-Val (SEQ ID NO: 11) -   MTT26: Gly-Ala-Glu-Asn-Trp-Met-Ser-Asp-Ile-Phe-Lys (SEQ ID NO: 12) -   MTT27-2:     Leu-Ala-Ala-Glu-Xaa-Gly-Phe-Ala-Val-Ala-Ala-Ala-Ala-Ile-Gly-Gly-Gly-Ile-Ile-Gly     (SEQ ID NO: 13) -   MTT28: Ser-Phe-Ile-Asn-Asp-Pro-Asn-Lys-Ile-Asp-Ala-Ile-Phe (SEQ ID     NO: 14) -   MTT141: Thr-Ala-Ser-Phe-Pro-Leu-Pro-Thr-Asn-Arg (SEQ ID NO: 15) -   MTT141-2: Phe-Pro-Gln-Leu-Arg (SEQ ID NO: 16) -   MT142: Ala-Asp-Phe-Gly-Trp-Gly-Lys (SEQ ID NO: 17) -   MTT291: Asp-Ala-Asp-Gln-Phe-Tyr-Asp-Leu-Leu-Pro-Pro-Ile-Pro-Pro (SEQ     ID NO: 18)

Example 5

Amplification of Gene Fragments Encoding Malonyl Transferase of Salvia

MT142 obtained in Example 4, the following primers were constructed.

-   MTT20-1: 5′-TA(T/C) GCI GCI GGI GA(T/C) TCI GTI CCl GT-3′ (I:     inosine) (SEQ ID NO: 19) -   MTT20-3: 5′-GTI CCl GTI ACI AT(A/T/C) GCI GC-3′ (SEQ ID NO: 20) -   ATCRr2: 5′-(T/C)TT ICC CCA ICC (A/G)AA (A/G)TC IGC-3′ (SEQ ID NO:     21)

PCR was carried out using cDNA prepared from salvia flowers as a template, with reactant solution having that following composition in a total amount of 100 μl; 1×TAKARA PCR buffer, 200 mM dNTPs, salvia cDNA 100 ng, MTT20-1 primer 1 pmol/μl, ATCRr2 primer 1 pmol/μl, TAKARA rTaq 2.5 units. Reaction was conducted at 96° C. for 1 minute, followed by 30 cycles with each cycle consisting of 1 minute at 96° C., 2 minutes at 42° C. and 3 minutes at 72° C., and further followed by 7 minutes at 72° C.

Nested PCR was carried out using this reaction product as a template, and using MTT20-3, ATCRr2 primers, with reactant solution of the same composition as described above. Reaction was conducted at 96° C. for 1 minute, followed by 30 cycles with each cycle consisting of 1 minute at 96° C., 2 minutes at 50° C. and 3 minutes at 72° C., and further followed by 7 minutes at 72° C. The PCR product obtained in this manner was subjected to subcloning, and its sequence was determined. As a result, in the deduced amino acid sequence of the reaction product of about 900 bp, partial amino acid sequences MTT141, MTT26, MTT27-2 (SEQ ID NO: 15, 12 and 13) beside with those used for design of primers were found. Thus, it was evident that the reaction product was a gene fragment encoding a purified protein.

Example 6

Isolation of cDNA Encoding the Malonyl Transferase of Salvia

A cDNA library derived from flowers of Salvia guaranitica was constructed using the λZAP II directional cDNA synthesis kit of Stratagene Co. in accordance with the method recommended by the manufacturer of the kit. About 200,000 clones of this library were screened using the washing condition (5×SSC, 0.1% SDS, 37° C.) with the DNA fragment of 889 bp obtained in Example 5 as a probe, and 10 clones were finally obtained as positive clones. These clones were classified into three kinds of groups, and the longest clones in these group are named as SgMaT1, SgMaT1′, and SgMaT2, respectively. Screening of the library was conducted in accordance with known methods (for example, Fujiwara et al., 1998, Plant J. 16, 421).

SgMaT1 and SgMaT1′ are 1419 bp and 1471 bp, respectively, and both lacked initiation methionine. Since SgMaT1 and SgMaT1′ exhibit an identity of 98% at amino acid level, they were considered as an allelic gene encoding the same enzyme. In the deduced amino acid sequence of SgMaT1, all the partial amino acid sequences of purified malonyl transferase determined in Example 4 were confirmed, although some are partially different. The partial difference is probably due to the difference of species of salvia used.

From these results, it became evident that SgMaT1 and SgMaT1′ genes encode an enzyme for transferring a malonyl group to a glycosyl group at the 5-position of anthocyanins. SgMaT2 has a cDNA of 1530 bp, which includes an open reading frame of 1260 bp encoding the full length. At the amino acid level, SgMaT1 exhibited 52% identify with SgMaT2. All of these genes exhibited a identify of 37 to 47% with acyl transferases of other plants.

In gentian, acyl transferases having different functions show identify of only 35 to 40%, even in the same varieties (Yonekura-Sakakibara et al., 2000, Plant Cell Physiol. 41: 495–502). Therefore, identity of 55% between SgMaT1 and SgMaT2 suggests, although the fact that the two genes are derived from the same variety is allowed for, that SgMaT1 and SgMaT2 are similar in function, and that SgMaT2 also catalyzes the reaction of transferring a malonyl group to anthocyanins. The nucleotide sequences of SgMaT1, SgMaT1′, and SgMaT2 are shown in SEQ ID NO: 1, 3, and 5, respectively, and the amino acid sequences deduced from these nucleotide sequences are shown in SEQ ID NO: 2, 4, and 6, respectively.

Example 7

Confirmation of Enzyme Activity of the Malonyl Transferase in Escherichia coli

A single colony of Escherichia coli having plasmid pSgMaT1 (including SgMaT1 gene at EcoRI, XhoI sites of pBluescriptSK⁻ (Stratagene), and capable of expressing an SgMaT1 gene product as a fusion protein with lac Z protein by addition of isopropyl-beta-thiogalactoside (IPTG)) introduced, was inoculated to LB medium containing ampicilin to a final concentration of 50 mg/L, and was precultured overnight while being shaked at 37° C. The preculture (2 ml) was inoculated to LB medium of 100 ml containing ampicilin, and was incubated at 30° C. until absorbance at 600 nm became 0.5. Then, IPTG was added to the culture medium to a final concentration of 1 mM. The culture was further maintained at 30° C. for 9 hours after the addition of IPTG, and then was collected. The collected cells were suspended in a buffer (0.1 M KPB, pH 7.0, 30 mM 2-mercaptoethanol, 1 mM EDTA, 0.1 mM PMSF, 0.1% TritonX-100), and disrupted by ultrasonic treatment while cooled on ice.

Enzyme activity was measured using a supernatant (soluble fraction) obtained after centrifuging. Escherichia coli containing only pBluescriptSK⁻ was processed in the same manner as control. Measurement of activity was conducted using shisonin as a substrate in accordance with Example 2.

In the reaction product from the reaction using the pSgMaT1 gene expression product, malonyl-shisonin was detected (Rt 12.2 minutes) in addition to shisonin (Rt 9.7 minutes), while only shisonin was detected in control. It was confirmed from this that the SgMaT1 gene encodes an enzyme having activity of transferring the malonyl group.

Example 8

Isolation of cDNA Encoding Malonyl Transferase Derived from Salvia (2)

A cDNA library of flower petals of salvia (Salvia splendens) was constructed using a ZAP-cDNA Synthesis Kit (Strategene Co.) with λZAP II (Strategene Co.) as a vector, in accordance with the method recommended by the manufacturer. Using SgMaT1 obtained in Example 6 as a probe, screening was carried out by the method described in Example 6. The clone with the longest cDNA was denoted by SsMaT1. This nucleotide sequence is shown in SEQ ID NO: 22, and the amino acid sequence deduced from this nucleotide sequence is shown in SEQ ID NO: 23. Considering the sequence, this cDNA is not considered to be a full-length cDNA.

SsMaT1 exhibited 92% identity with SgMat1, and 52% identity with SgMaT2 at the amino acid level.

Similarly, the same library was screened using SgMaT2 as a probe, and SsMaT2 was obtained. This nucleotide sequence is shown in SEQ ID NO: 24, and the amino acid sequence deduced from this nucleotide sequence is shown in SEQ ID NO: 25.

SsMaT2 exhibited 53% identity with SgMat1, 96% identity with SgMaT2, and 52% identify with SsMaT1 in amino acid level.

Example 9

Isolation of cDNA Encoding the Malonyl Transferase Derived from Perilla

Young red leaves were collected from perilla (Perilla frutescens), and starting from this material, a cDNA library was constructed using a ZAP-cDNA Synthesis Kit (Strategene Co.) with λZAP II (Strategene Co.) as a vector, in accordance with the method recommended by the manufacturer. As in Example 8, this library was screened using SgMaT1 as a probe, and the clone having the longest cDNA among obtained clones was denoted by PfMaT1. The nucleotide sequence of PfMaT1 is shown in SEQ ID NO: 26, and the amino acid sequence deduced from the nucleotide sequence is shown in SEQ ID NO: 27.

PfMaT1 exhibited 67% identity with SgMaT1, 57% identity with SgMaT2, 65% identity with SsMaT1, and 57% identity with SsMaT2 in amino acid level.

Example 10

Isolation of cDNA Encoding the Malonyl Transferase Derived from Lavender

A cDNA library of lavender (Lavendula angustifolia) was constructed using a ZAP-cDNA Synthesis Kit (Strategene Co.) with λZAP II (Strategene Co.) as a vector, in accordance with the method recommended by the manufacturer. Using SgMaT2 obtained in Example 6 as a probe, screening was carried out by the method as described in Example 6, and LnMaT2 was obtained. This nucleotide sequence is shown in SEQ ID NO: 28, and the amino acid sequence deduced from this nucleotide sequence is shown in SEQ ID NO: 29.

LnMaT2 exhibited 53% identity with SgMaT1, 65% identity with SgMaT2, 51% identity with SsMaT1, 64% identity with SsMaT2, and 56% identity with PfMaT1 in amino acid level.

Example 11

Expression of S. splendens MaT1

A primer for introducing a BamHI site at the 5′-end of the SsMaT1 gene obtained in Example 8 (Primer #1: 5′-GGA TCC ATC GAG GGA CGC ATG ACA ACA ACA ACA AC-3′ (SEQ ID NO: 30)), a primer for introducing a BamHI site at the 3′-end of the SsMaT1 gene (Primer #2: 5′-GGA TCC TTA CAA TGG TTC GAC GAG CGC CGG AGA-3′ (SEQ ID NO: 31)), and a primer for deleting the BamHI site in the SsMaT1 gene (Primer #3: 5′-G GAC CCG CCG ATA CCG GAA AAT TAC TTC-3′ (SEQ ID NO: 32)) were synthesized. The primer #1 was designed such that a Factor Xa cleavage site (Ile-Glu-Gly-Arg) is encoded just before the SsMaT1 initiation codon, methionine.

A first PCR reaction was carried out using Primer #2 and Primer #3 with the plasmid (pBK-CMV-SsMaT1) having SsMaT1 cDNA introduced at multi-cloning sites (EcoRI, XhoI) of pBK-CMV phagemid vector (Toyobo Co.) as a template (composition of reactant: pBK-CMV-SsMaT1 100 ng, 1×pfu buffer (Stratagene Co.), 200 μM dNTPs, 1 μM Primer #2, 1 μM Primer #3, 2.5 U pfu polymerase (Stratagene Co.); reaction condition: 96° C. 2 minutes, (96° C. 1 minute, 70° C. 1 minute, 72° C. 3 minutes) ×30 cycles, 72° C. 7 minutes), and a PCR product (about 500 bp) was obtained.

Using the double strand DNA fragment of SsMaT1 obtained as the first PCR product and Primer #1, a second PCR reaction was carried out (composition of reactant: pBK-CMV-SsMaT1 100 ng, 1×pfu buffer, 200 μM dNTPs, 1 μM Primer #1, the first PCR product 100 ng, 2.5 U pfu DNA polymerase (Stratagene Co.); reaction conditions: 96° C. 7 minutes, (96° C. for 2 minutes, 70° C. for 1 minute, 72° C. for 7 minutes) ×30 cycles, 72° C. for 10 minutes).

The second PCR product was subjected to A-tail addition (the second PCR product 100 ng, 1×ExTaq buffer, 2 mM dATP, TAKARA ExTaq; 70° C., 30 minutes), and was cloned to pCR2.1-TOPO vector (Clonetech Co.). As a result, a plasmid for inserting a full-length SsMaT1 was obtained (pCR2.1-SsMat1). Using a DNA sequencer, it was confirmed that an incorrect nucleotide was taken into the DNA sequence of the SsMaT1 gene due to the PCR operation.

The pCR2.1-SsMaT1 was completely digested with BamHI, and a produced DNA fragment of about 1400 bp was recovered. This DNA fragment was subcloned to the BamHI site of Escherichia coli expression vector pQE-30 (QIAGEN Co.), and was denoted by pQE-30Xa-SsMaT1.

Expression of SsMaT1 in Escherichia coli containing pQE-30Xa-SsMaT1 was conducted in accordance with the method described in Example 7. Measurement of enzyme activity was conducted in accordance with the method described in Example 2.

Extract from Escherichia coli expressing the SsMaT1 gene was used to measure enzyme activity, and it was confirmed that malonyl-shisonin was produced in addition to shisonin. Thus, it was confirmed that the SsMaT1 gene encodes a protein having activity for transferring a malonyl group to a glycosyl group at 5-position of flavonoids.

When acetyl CoA, methylmalonyl CoA, or succinyl CoA was used in place of malonyl CoA as a substrate, a new peak in addition to shisonin was observed in column chromatography using HPLC, indicating that SsMaT1 has activity for transferring these substrates to shisonin.

Example 12

Expression of P. frutescens MaT1

As in Example 7, using a plasmid constructed such that the PfMaT1 gene obtained in Example 9 can be expressed as a fusion protein fused with LacZ protein, the PfMaT1 gene was expressed in Escherichia coli as in Example 7, and enzyme activity was measured. Measurement of enzyme activity was conducted in accordance with the method described in Example 2.

An extract from Escherichia coli expressing the PfMaT1 gene was used to measure enzyme activity, and it was confirmed that malonyl-shisonin was produced in addition to shisonin. Thus, it was confirmed that the PfMaT1 gene encodes a protein having activity for transferring a malonyl group to a glycosyl group at 5-position of flavonoids.

INDUSTRIAL APPLICABILITY

It has been made evident for the first time by the present invention that an aliphatic acyl transferase is involved in the control of flower colours. Flower colour can be altered by expressing this protein in flower petals for modifying anthocyanins. As an aliphatic acyl transferase, any gene which encodes a protein having the same enzyme activity in other organisms may be used in addition to the above-described genes derived from salvia, perilla plant, and lavender. 

1. An isolated or synthesized gene encoding a protein which comprises an amino acid sequence exhibiting at least 65% identity with an amino acid sequence selected from the group consisting of SEQ ID NO: 2, 23, and 27 and wherein the protein has an activity to transfer a malonyl group to a glycosyl group at the 5-position of anthocyanins.
 2. The isolated or synthesized gene according to claim 1, wherein the gene encodes a protein which comprises an amino acid sequence selected from the group consisting of SEQ ID NO: 2, 23, and
 27. 3. The isolated or synthesized gene according to claim 1, wherein the gene encodes a protein which comprises an amino acid sequence exhibiting identity of at least 80% with an amino acid sequence selected from the group consisting of SEQ ID NO: 2, 23, and
 27. 4. A vector comprising a gene according to claim
 1. 5. A host transformed by a vector according to claim
 4. 6. A transgenic plant comprising a gene according to claim 1 introduced therein, or offspring or tissue thereof comprising said gene.
 7. A cut flower of the transgenic plant according to claim 6 or the offspring thereof comprising said gene.
 8. A method for altering the colour of flowers by introducing a gene according to claim 1 into the genome of a plant containing anthocyanins and causing constitutive or tissue-specific expression of said gene in the plant.
 9. A method for blueing the colour of flowers by introducing a gene according to claim 1 into the genome of a plant containing anthocyanins and causing constitutive or tissue-specific expression of said gene in the plant. 